1. Technical Field
The present invention relates to a semiconductor device having a plurality of semiconductor devices and, more particularly, to the semiconductor device in which a plurality of power elements are controlled by a control element.
2. Background Art
A power element is a semiconductor element which supplies electric power to a load. As the power element, there are a power transistor, a power MOSFET (metal-oxide-semiconductor field-effect transistor), an IGBT (insulated gate bipolar mode transistor) and so on. The control element, such as control ICs and CPU, is the semiconductor device by which the power element is controlled.
Recently, in order to further advancement in densification and miniaturization of the semiconductor device, there is used a multiple-chip package where a chip for a semiconductor element (hereinafter simply referred to as a chip) such as a plurality of integrated-circuit elements and an individual semiconductor element, is packaged in a single package. Though there is used a circuit base plate such as a printed board, serving as a on-chip substrate in this type of package, a lead frame is often utilized for a general use. The lead frame is made of Cu (copper) or an alloy mainly composed of Cu. In the lead frame, there are equipped therein an island for placing the chip thereon, a pin or lead for supporting the island, and so on. The chip is placed on the circuit base plate or lead frame, and is resin-packaged, thereby constituting a prescribed circuit.
Referring to FIG. 1 and FIG. 2, described is a semiconductor device which constitutes an H bridge circuit for driving a motor.
FIG. 1 is a top view of the semiconductor device (element) in the conventional practice. FIG. 2A and FIG. 2B are cross sectional views substantially taken along lines IIA--IIA and IIB--IIB shown in FIG. 1, respectively. In the semiconductor shown in FIG. 1, the chip is formed by placing it on the lead frame. The lead frame 3 has island 82 for mounting the chip thereon; in FIG. 1, there are five islands 32 to mount fives chips, and a power element chip 1 is connected and fixed to the island 32 by a solder 4 or the like (FIG. 2A and FIG. 2B). Referring to FIG. 1, a control element chip 2 is provided on a centrally located island 32, and is fixed with the solder 4. In order to electrically connect a lead 33 of the lead frame 3 to each chip, a joint electrode (not shown) formed in each chip and an inner lead portion in an end of the lead 33 are connected with a bonding wire 5 (FIGS. 2A and 2B) such as an Au wire.
After chips 1, 2 are fabricated on the lead frame 3 in the manner described above, the lead frame 3 is assembled to a mold forming metal pattern along with a heat-radiating plate 6 such as Cu. Then, after performing a transfer mold formation, a packaging process is carried out utilizing a thermoplastic resin such as an epoxy resin. Thereafter, a short-circuit portion of the lead frame 3 is cut and formed. As a result thereof, the plastic package 7 completely covers the chips 1, 2 and islands 32, and the heat-radiating plate 6 (FIGS. 2A and 2B) is placed under the plastic package 7.
Referring to FIGS. 2A and 2B, the upper surface and side face of the heat-radiating plate 6 are covered with the package 7, and the underside of the heat-radiating plate 6 is exposed. The inner lead portion to which the bonding wire 5 of the lead 33 is connected, is resin-packaged, whereas an outer lead portion 8 (FIG. 2B) which is electrically connected to a circuit in other side, is exposed from the plastic package 7. The outer lead 8 is often in the form of being bent so that it may be easily mounted to the circuit based plate and the like.
In the semiconductor devices presenting these multiple-chip package configuration, a problem is caused because both the power elements and the control element coexist on the same plastic package. Since two different types of chips coexist thus, for example, an environmental temperature of the control element is affected by the heat generated by the power element upon energization thereof. As a result thereof, a characteristic of the control element is changed unwantedly, so that a guarantee accuracy for each characteristic in an overall device is deteriorated. For example, it is to be noted that a Zener voltage In the Zener diode utilized as a reference voltage supply among control elements, and the resistance of detection resistance for detecting the current are generally temperature-dependent. Therefore, the more the degree in decrease of the environmental temperature becomes, the greater the unwanted characteristic difference becomes.